- RHIC, PHENIXPHENIX Pad Chambers

- Net-Charge FluctuationsPredictionsPHENIX AnalysisComparison to simulations

OUTLINEOUTLINE

Relativistic Heavy Ion Collider (RHIC)Relativistic Heavy Ion Collider (RHIC)Au+Au Collisions 200 AGeV

~ 400 Members

57 Institutions

12 Countries

~ 400 Members

57 Institutions

12 Countries

Collaboration

Central Magnet

Beam-BeamCounters

Muon ArmSpectrometers Central Arm

Spectrometers

Central Arms

Pad Chambers

Charged ParticleTracking

Electron, Photon Detection

Hadron Identification

Pad Chambers- Multi-Wire Proportional Chambers

- Fine Granularity Pixel Pad Readout

- Provide 3D Space Points for Track Recognition

Pad Chambers- Multi-Wire Proportional Chambers

- Fine Granularity Pixel Pad Readout

- Provide 3D Space Points for Track Recognition

- 172,800 Readout Channels

- Chip-On-Board Technique

Readout Cards (ROCS) Placed on the Chambers

- Data Transfer via Fiber Optic Links

Readout Card (ROC)

Event Display

CentralAu+Au

Collision

~ 400tracks in

central arms

QUARK GLUON PLASMAQUARK GLUON PLASMA

DECONFINEMENTDECONFINEMENT

PHASETRANSITION

Signals?

charge more evenly spread in plasma,due to the fractional charges of quarks

Hadron Gas QGP

NET-CHARGE FLUCTUATIONS

Event-by-Event Fluctuationsof Net Electric Charge

in Local Regions of Phase Space

Decrease of Fluctuationsproposed as a signal for the QGP

Predictions range up to an 80% reduction

For each event:

Let n+ and n- denote the nr of positive and negative particles, respectively.

Net charge

Nr of charged particles

A very simple measure of net-charge fluctuations is then

since the variance of Q scales with nch .

Hadron gas, no correlations:

QGP, no correlations:

Hadronized QGP, (Jeon & Koch paper):

But charge is a globally conserved quantityInstead of v(Q)=1, the hadron gas scenario yields:

where pa is the fraction of charged particles falling into the detector acceptance among all charged particles in the event.Also charge asymmetry, , has been taken into account.

where p+ and p- are the probabilities that aparticle is positive and negative, respectively.

A better measure of net-charge fluctuations is

which yields

in the hadron gas scenario.

NET CHARGE FLUCTUATIONS

RHIC 1st run period

GeVsNN 130

~ 500 000 events

|zvertex| < 17 cm

pT > 200 MeV/c

Acceptance window defined around midpoint of detector arm

Reduction not as large as predicted for QGPConsistent with RQMD simulation

Global ChargeConservation

10% most central events

Fluctuations independent of centrality

NET CHARGE FLUCTUATIONS

RHIC 2nd run period

GeVsNN 200

~ 850 000 events

|zvertex| < 17 cm

pT > 200 MeV/c

pT < 2 GeV/c

dc+pc1

Clear centrality dependence

Hijingsimulations

r = 50

Using efficiency and charge asymmetry differences between track association cuts are removed

( 1 – pa )

Percentages show the fraction of particles generated withthe toy model. The rest is from pure global charge conservation.

Gaus(0.2,0.1)

Toy model of hadronization from QGP

- A very intriguing net-charge fluctuation centrality dependence is seen at 200 A GeV , not explainedby purely hadronic models.

- A comparison with a toy model of hadronization froma QGP shows that the initial predictions on a very drastic decrease of net-charge fluctuations may have been too optimistic.

- A large data sample at 200 A GeV is right now being prepared for analysis. Higher statistics and even more stable conditions during data taking will improve the measurements further.

SUMMARYSUMMARY